A year ago, President Obama fully intended to reduce the U.S. military footprint in Afghanistan to 1,000 troops, who would focus on protecting our embassy in Kabul. That plan has been replaced with a new policy that commits U.S. forces to Afghanistan into the future, training the Afghan military and combating terrorist forces.

“While America’s combat mission in Afghanistan may be over, our commitment to Afghanistan and its people endures,” Obama said. He added: “It’s the right thing to do.” [...]

Obama said the 9,800 U.S. troops currently in Afghanistan would stay through most of 2016, and then be reduced to 5,500 troops working out of military bases in Bagram, Jalalabad and Kandahar.

Towards the end of his remarks, as the president prepared to leave the room, a reporter asked if he's disappointed by the need to make this change in policy, Obama said he isn't.

"[Y]ou have a situation [in Afghanistan] where we have clarity about what our mission is," the president said. "We’ve got a partner who wants to work with us. We’re going to continually make adjustments to ensure that we give the best possibilities for success. And I suspect that we will continue to evaluate this going forward, as will the next president."

Those last three words -- "the next president" stood out because they served as a reminder of the political circumstances. President Obama inherited a war in Afghanistan, and his successor will do the same.

To be sure, we're describing a quantitatively different kind of military commitment. Five years ago, there were 100,000 U.S. troops in Afghanistan. Over 90% of those American servicemen and women have already been withdrawn, and under the policy Obama outlined today, the number will shrink further.

But an extended mission is still an extended mission, and thousands of American troops in Afghanistan -- for the indefinite future -- still represents an enormous national-security challenge for the next U.S. administration.

All of which creates a new question that none of the presidential candidates in either party has had to answer: what's your plan for Afghanistan?

I checked the transcripts for each of the three prime-time debates that have been held this year, and the number of instances in which candidates even mentioned Afghanistan in passing can be counted on one hand.